1. Field of the Invention
The present invention relates to a display driving apparatus, a display apparatus having the display driving apparatus, and a drive control method for the display apparatus.
2. Description of the Related Art
An organic EL (Electro-Luminescence) device is a light emitting device that has a fluorescent or phosphorous organic compound which is excited by application of an electric field, and emits light according to the applied current.
Light emitting devices of this kind have been drawing attention as next generation display devices. The organic EL or other devices are used in a pixel, and a display apparatus based on a matrix of such pixels have been a subject of ongoing research and development.
The organic EL device is a current drive device, and emits light with a luminance proportional to the flowing current. A display apparatus having such organic EL devices has a drive transistor formed by a field effect transistor (thin film transistor) at each pixel. The drive transistor controls the current value of the current to be supplied to the organic EL device according to the voltage applied to the gate of the transistor.
At each pixel, a capacitor is connected between the gate and source of the drive transistor. A voltage corresponding to a video signal externally supplied is written in the capacitor which holds the voltage.
When a voltage is applied between the drain and source of the drive transistor, the drive transistor supplies the current to the organic EL device while controlling the current value with the voltage held by the capacitor treated as a gate-source voltage (hereinafter called “gate voltage”) Vgs.
The current value of the current supplied to the organic EL device from the drive transistor is determined according to the value of the gate voltage Vgs and the characteristic values of the drive transistor (threshold voltage Vth and current amplification factor β).
It is known that the threshold voltage Vth varies due to the drive history or the like of the pixels. When the threshold voltage Vth is changed by the drive history or the like, the luminance of the organic EL device varies even with the same gate voltage Vgs. This degrades the display quality.
Therefore, aiming at improving the display quality, now underway is the development of display devices with pixels using organic EL or other light emitting devices, in which the value of the threshold voltage Vth of each pixel is obtained and the obtained value is used to correct the value of the voltage to be applied between the gate and source of the drive transistor in accordance with a video signal.
While the current amplification factor β is not changed much by the drive history, it may vary among pixels due to, for example, the fabrication process factor.
With a variation in current amplification factor β between pixels, degrading of the display quality originating from the variation in current amplification factor β between pixels is not overcome even if the voltage value of the voltage to be applied between the gate and source of the drive transistor is corrected with the acquired value of the threshold voltage Vth of each pixel.